Lapping machine and method

ABSTRACT

A lapping machine employing first and second lapping discs mounted coaxially for rotation and having first and second air cushion means for biassing the discs outwardly with respect to each other against the inwardly biassing force of spring means engaging the outer sides of the discs with the air cushion means being mounted for axial adjustment with respect to each other to consequently adjust the axial distance between the discs and with such adjustments being enabled by means of adjustable shift plates supporting the air cushion means and movable toward and from each other by means of first and second dovetail wedge block couples located on each end of said plates so that relative movement of the plates with respect to each other causes the plates to move toward or away from each other.

United States Patent Raickle [451 Apr. 4, 1972 [54] LAPPING MACHINE AND METHOD [72] lnventor: John A. Raickle, Hopewell Junction, N.Y. fgfggfglgfg9gisssg [73] Assignee: Industrial Micronics Incorporated, A n y- Fenwick & Lawrence Leesburgh, Va. [57] ABSTRACT [22] Filed: Apr. 23, 1969 A lapping machine employing first and second lapping discs [21] P No; 818,501 mounted coaxially for rotation and having first and second air cushion means for biassing the discs outwardly with respect to [52] US. Cl .5 1/109, 51/1 1 1, 51/1 19 each other against the r ly ing force of spring means 51 Int. Cl ..B24b 7/02 engaging P Outer sides discs with whim 58 Field of Search ..308/9; 51/109, 111-118, means bemg mmmed axial adjustment wlth 68pm 51 19 each other to consequently adjust the axial distance between the discs and with such adjustments being enabled by means of ad'ustable shift lates su ortin the air cushion means and [56] References Cited mt ivable toward and fror n each other by means of first and UNITED STATES PATENTS second dovetail wedge block couples located on each end of said plates so that relative movement of the plates with respect 2,882,651 4/1959 Price ..51/118 to each other causes the plates to move toward or away from 3,041,793 7/1962 Shimizu ..51/109 X each other. 3,223,463 12/1965 Porath ..308/9 3,380,198 4/1968 Takada ..51/111 X 18 Claims, 7 Drawing Figures PATENTEDAPR 4 I972 SHEET 1 OF 4 INVENTOR Ion-m mcwaa mfm iw go m ATTORNEYS PATENTEDAPR 4 I972 SHEET 2 [1F 4 INVEN'I OR Town A .RAacKLE BY g QAALL 1%7 D i ATTORNEYS mascu- PATENTEDAPR 4 1972 SHEET 3 [1F 4 INVEN] OR JOHN A. Nc-KLE 02mm as ATTORNEY 8 PATI EDAPR 41972 3,653,160

SHEET Q 0F 4 INVENTOR MN Ewe sa a gmmc,

ATTORNEYS LAPPING MACHINE AND METHOD BACKGROUND OF THE INVENTION This invention is in the field of polishing and smoothing machines and is specifically directed to a lapping machine for providing exceptionally smooth lapped surfaces.

A great need for highly accurate lapping machines capable of providing extremely smooth lapped surfaces has been created by the great advances in technology made during recent years. For example, semi-conductors, piezoelectric crystals and other solid-state electronic components must be dimensioned to extremely close tolerances in order to provide the mandatory highly accurate electrical characteristics needed in sophisticated electronic circuitry. Such dimensioning requires an extremely smooth lapping or polishing of the surfaces of many of such devices in order that the required high dimensional accuracy can be obtained.

Moreover, there has always existed a need for highly accurate gauge blocks, micrometers, and other measuring equipment with the degree of accuracy being obtainable being limited largely by the smoothness to which the measuring surfaces can be ground. Consequently, there has been a continuous effort by those skilled in the art to provide means capable of giving greater smoothness to lapped surfaces used in a wide variety of devices.

An example of one approach toward the problem of providing highly accurate solid-state electronic components such as piezoelectric crystals, quartz crystals and the like is found in US Pat. No. 3,395,494. This patent is directed to a lapping machine in which elements to be polished are placed between two lapping discs one of which is rotated with respect to the other and with the element being lapped serving to support the upper lapping disc. The device shown in this patent is limited to the lapping of thin wafers and similar elements and cannot be employed for lapping elements such as micrometer anvils, gauge blocks and the like.

Another shortcoming of the device shown in this patent is that it fails to provide any means capable of accurately adjusting the force of engagement between the lapping disc and the wafers being lapped.

The instant invention, on the other hand, provides a great improvement over the prior known devices in that it enables the achievement of much more smooth lapped surfaces than have been obtainable heretofore. For example, the instant invention enables the polishing of steel to such a degree that the highest ridges in the steel only extend in the order of 0.00001 inch above the base of the lapped surface. This high degree of accuracy compared with the prior known devices in which the minimum height of the ridges that could be obtained was in the order of0.000l inch.

Moreover, the instant invention is highly versatile and can be employed for simultaneously lapping the surfaces of measuring devices such as micrometer anvils and fixed linear gauges of substantial dimensions while retaining the capability of lapping small wafers, crystals and the like employed in solid-state electronic equipment.

SUMMARY OF THE INVENTION Therefore, it is the primary object of this invention to provide a new and improved lapping machine having the ability to provide extremely smooth lapped surfaces on a wide variety of objects.

Obtainment of the object of this invention is enabled through the provision of first and second parallel co-axial lapping discs having a lapping surface on their outwardly facing planar sides and mounted for rotation upon a common drive shaft. The two lapping discs are biassed outwardly away from each other by an air cushion bearing associated with the inner planar side of each disc. The biassing force of the air bearing is counterbalanced by a spring means so as to position the lapping discs a desired distance apart. Adjustment of the distance between the lapping discs is enabled by means of adjustable shift plate means that are connected in a unique LII manner by a pair of wedge couples so as to remain absolutely parallel with respect to each other during and following adjustment of the plates for effecting adjustment of the position of the lapping discs. Maintenance of the parallel condition between the air cushion support plates is enabled through the provision of a pair of dovetailed wedge couples one of which is located on each end of the plates. The wedge couples connect the shift plates and adjust the lateral distance between the plates upon linear reciprocation of the plates with respect to each other.

The employment of the air cushion bearings supported on the adjustable shift plates enables the lapping surface on the outer side of each lapping disc to be engaged at the surface being lapped very lightly with a kiss touch so as to obtain maximum smoothness and accuracy. Moreover, the fact that the lapping discs are moved by virtue of air pressure is of par ticular value in that vibration and the like are not transmitted directly to the lapping discs.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevational view of a preferred embodiment of the invention illustrating the lapping discs in inwardly adjusted relatively close position and with portions broken away for clarity;

FIG. 2 is a sectional view taken along lines 2-2 of FIG. 1;

FIG. 3 is a sectional view taken along lines 3-3 of FIG. 2;

FIG. 4 is a sectional view taken along lines 4-4 of FIG. 2 with the parts being in a different position of operation in which the lapping discs are spaced a maximum distance apart;

FIG. 5 is a sectional view taken along lines 5-5 of FIG. 1;

FIG. 6 is a sectional view taken along lines 6--6 of FIG. 1;

FIG. 7 is a sectional view similar to FIG. 6 but illustrating an alternate embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Attention is initially invited to FIG. 1 of the drawings which illustrate the preferred embodiment 20 of the invention. A main frame generally designated 22 formed of rigid metal plates for structural stability is provided with a floor plate 23 from which extend a pair of vertical standards 24 and 26 each of which has a rotary bearing 28 attached to its uppermost end for providing support for a rotatable drive shaft 30 extending through the bearings. Drive shaft 30 is driven by the output of a conventional step-down electrically driven transmission or variable speed motor (not shown).

First and second vertical frame plates 32 and 34 extend upwardly from floor plate 23 and are connected across their upper ends by a horizontal apertured bracket plate 36. A central aperture 38 of rectangular configuration is provided in bracket plate 36 for a purpose to be discussed hereinafter.

A first lapping disc 40 and a second lapping disc 42 are connectingly attached to and supported by the drive shaft 30 for rotation therewith. However, the first and second lapping discs 40 and 42 are capable of axial movement along shaft 30 by virtue of the fact that they are provided with a square axial opening which matingly fits over squared portions 44 formed in the drive shaft 30 as best illustrated in FIGS. 1 and 6. Consequently, rotation of drive shaft 30 serves to rotate the first and second lapping discs 40 and 42 while the lapping disc remains fully capable of axial movement along the shaft. The extent of axial movement of the lapping discs is limited so that they are always on the squared portions 44.

Each lapping disc is provided with an annular groove 46 on its outer face which serves to divide the outer face into an outer peripheral portion formed of a lapping surface 48 having lapping compounds thereon and an inner surface 50 (FIG. 2) extending inwardly from the annular groove 46 and terminating at the squared opening which receives the squared portion 44 of shaft 30. The lapping surface 48 extends between the outer edge of the annular groove 46 and terminates at the circumference of the disc as best illustrated in FIG. 2. Each lapping disc is provided with an inner, planar, smooth face 52 (FIG. 1), the purpose of which will become apparent hereinafter.

Each lapping disc is provided with an air cushion biassing means for biassing the lapping discs outwardly away from each other. Specifically, the first lapping disc 40 is provided with a first air cushion bearing means 54 and the second lapping disc 42 is provided with a second air cushion bearing means 56 as shown in FIG. 1.

Air cushion bearing 54 has an annular groove 58 which faces surface 52 of disc 40 as best illustrated in FIG. 5. Pressurized air is provided to annular groove 58 by a first air hose 60 (FIG. which communicates with the annular groove 58 in a manner to be discussed in greater detail hereinafter.

The second air cushion bearing 56 is provided with an annular groove 62 which faces the surface 52 of the lapping disc 42 as best illustrated in FIGS. 1, 2 and 5. Pressurized air is provided to the annular groove 62 by means of a second air hose 64 communicating with the annular opening 62 in a manner to be discussed hereinafter.

The first and second air cushion bearings 54 and 56 are connected by a first dove-tailed wedge couple generally designated 66. Wedge couple 66 is formed of a first wedge 68 unitarily extending from the second air cushion bearing 56 as best illustrated in FIG. 1. The first wedge 68 is provided with a rearwardly extending male dovetail member 72 which is received in a female dovetail slot 74 formed in the second wedge 70. The male dovetail member 72 is maintained in the snug relationship in the female dovetail slot 74 by means of a shim 76 held in position by a set screw 78. An opening 80 (FIG. 5) extends through the first air cushion bearing 54, the first wedge 68, the male dovetail member 72, the second wedge 70 and the second air cushion bearing 56 with the shaft 30 extending through the opening 80 as shown.

The outward extent of the male dovetail member 72 is defined by a plane 82 of sliding contact between the first wedge 68 and the second wedge 70 which also defines the bottom of the female dovetail slot 74. Plane 82 is oriented at an angle with respect to shaft 30 as shown in FIG. 4. Similarly, that portion of the first wedge 68 on each side of the male dovetail member 72 as shown in FIG. 5 is oriented in another plane of sliding contact 84 that is parallel to plane 82. The orientation of the sliding contact planes 82 and 84 is such that movement of either of the wedges 68 or 70 transversely with respect to the axis of shaft 30 will cause the air cushion bearings 54 and 56 to be shifted outwardly or inwardly along the axis of shaft 30 with respect to each other.

Means for moving the first and second wedges transversely with respect to the shaft are provided in the form of a first shift plate 86 as illustrated in FIG. 6 and embracingly received over the first wedge 68 adjacent the air cushion bearing 54 and a second shift plate 88 embracingly received over the second wedge 70 adjacent the second air cushion bearing 56. Vertical movement of either of the shift plates with respect to the other will consequently result in relative movement of the associated wedges so as to consequently shift the air cushion bearings either toward or away from each other in a direction along the axis of shaft 30. In actuality, the shifting movement of the shift plates with respect to each other is effected by means for shifting both plates in opposite directions simultaneously; this means for shifting the shift plates will be discussed hereinafter.

Communication between air hose 60 and annular groove 58 is provided by a passageway 90 extending through the first wedge 68 and the air cushion bearings 56 as shown in FIG. 5, for example. Similarly, communication between the air hose 64 and the annular opening 62 formed in the second air cushion bearing 56 is provided by a passageway 100 extending through the second wedge 70 and the second air cushion bearing 56 as best illustrated in FIGS. 1 and 4. Pressurized air at sufficiently high pressure is injected from hoses 60 and 64 into the annular openings 58 and 62 so as to be forced outwardly radially between the bearings and the inner surfaces of the lapping discs to create an air cushion between the air cushion and their associated lapping discs in an obvious manner. Therefore, the outflow of air creating the air cushion prevents metal-tometal contact between the lapping discs and their associated bearing means. Consequently, the air pressure in the annular openings 58 and 62 serves to respectively urge the associated lapping discs outwardly away from each other. In other words, the pressure in annular opening 58 serves to urge annular disc 40 to the left as illustrated in FIG. 1 while the pressure in annular opening 62 serves to urge lapping disc 42 to the right as illustrated in FIG. 1.

It is desirable that the parts for effecting axial movement of the air cushion bearings should operate with as little play as possible. For this reason, a bias rod 102 is mounted for movement in a cylinder 104 attached to the second shift plate 88 as shown in FIG. 1. Bias rod 102 is biassed to the left by a coil spring 106 extending between the right end of the rod and the side of plate 88 in an obvious manner. Consequently, bias rod 102 always engages the side of plate 86 so as to bias plates 86 and 88 apart and to retain a play-free relationship between the first wedge 68 and the second wedge 70.

Resistance to the outwardly biassing force of the pressurized air within annular openings 58 and 62 is provided by a pair of spring bias cups 108 located adjacent the outer sides of the lapping discs 40 and 42. Each of the spring bias cups is biased inwardly by a coil compression spring 110 extending between the cup and a collar 114 fixed to shaft 30 in a conventional manner by a set screw 116. Cups 108 are guided for axial movement by a cylindrical bushing 118 within a bore in their interior and encircling the shaft 30 as shown in FIG. 1.

Means for shifting the shift plates 86 and 88 perpendicularly with respect to the shaft 30 and in different directions with respect to each other are shown in FIG. I mounted beneath the floor plate 23. This shifting means includes a second or lower wedge couple 120 formed of a first lower wedge 122 and a second lower wedge 124 which are engageable with each other in essentially the same manner as wedges 68 and 70. The first lower wedge 122 is affixed to the lower end of first shift plate 86 and the second lower wedge 124 is afr'ixed to the lower end of the second shift plate 88. The first lower wedge 122 is provided with a male dovetail member 126 (FIG. 3) received within a mating female dovetail slot 128 formed in the second lower wedge 124. The dovetail connection between the first and second lower wedges 122 and 124 is essentially identical to the connection between the first wedge 68 and second wedge 70 as discussed previously. For example, the outermost surface of the male dovetail 126 engages the bottom of the female dovetail slot 128 along a plane of sliding contact 130 that is parallel to planes 82 and 84 associated with the upper wedge couple 66. Similarly, the lower or second wedge couple 120 has a second plane 132 of sliding contact engagement at which legs 134 on opposite sides of the female dovetail slot 128 engage the sides of wedge 1-2 on opposite sides of the male dovetail I26. Plane 132 is parallel to the plane 130 which is parallel to the planes of sliding contact 84 and 82 of the upper wedges 68 and 70. Therefore, since the angle of engagement between the first lower wedge 122 and the second lower wedge 124 is parallel to the angle of engagement between the upper wedges 68 and 70, a parallel relationship between the first shift plate 86 and the second shift plate 88 is constantly maintained.

Shifting of the shift plates 86 and 88 with respect to each other in a direction perpendicular to shaft 30 is enabled by means of a rotatable knob 135 attached to the end of an adjustment shaft 136 which is supported adjacent its outer end in a side wall 137 of the frame 22 as shown in FIG. 2 and is supported inwardly by means of a depending bracket bearing 138 extending downwardly from the floor plate 23. A bevel gear 140 is fixed to the end of adjustment shaft 136 to engage a driven bevel pinion gear 142 fixed to the middle of a threaded rod 144. The threads formed in rod 144 above the driven pinion 142 are of reverse character from the threads formed in the rod below the driven pinion 142. In other words, the threaded portion above the pinion is either of right or left hand nature while the threaded portion below the pinion is of opposite nature.

Driven pinion 142 and rod 144 are supported from floor plate 23 by a horizontal support plate 146 that is connected between a pair of pillars 148 depending beneath plate 23 as shown in FIG. 1. Driven pinion 142 is keyed to rod 144 and has a shank portion 143 which is received in a mating circular opening in support plate 146. A locking collar 145 on the end of shank 143 maintains gear 142 in position on plate 146 so that movement of gear 142 and rod 144 is limited solely to rotary movement.

Lateral stability of the adjustment means mounted beneath floor plate 23 is provided by a main vertical plate 160 (FIG. 2) connected to a main horizontal plate 162 bolted to the floor plate 23. Two brace plates 164 are connected to plates 160 and 162 to provide a uniquely rigid and strong construction. A pair of guide tracks 166 are connected along opposite edges of the main vertical plate 160 as shown in FIG. 3. The guide tracks 166 are L-shaped to provide an interior rectangular opening 168 formed between one leg of the guide track and the side of the main plate 160. Each of the openings 168 receives one leg of an L-shaped angle plate 170, the other side of which is connected to one or the other of the shift plates 86 or 88 as shown in FIG. 3. It should be noted that the relationship between the tracks 168 and the angle plates 170 is such that the opening 168 is of sufficient dimensions to permit guide plates 86 and 88 to move apart from each other as shown in FIG. 3 but to preclude such from any movement to the left or right as shown in said Figure. It is necessary that the shift plates 86 and 88 be able to move apart during adjustment of the lapping disc for reasons to be made more apparent hereinafter.

Relative vertical movement of the shift plates 86 and 88 with respect to each other is enabled by a first threaded shift block 172 threaded on the upper portion of rod 144 and a second threaded shift block 174 threaded on the lower end of rod 144 as best illustrated in FIG. 2, Since the portions of the rod 144 upon which blocks 172 and 174 are respectively threaded are of opposite thread types, rotation of the rod will cause the blocks 172 and 174 to move in opposite directions. The first threaded shift block 172 is provided on its outer end with a pin 175 that is received in a horizontal slot formed in the wedge 122 and the edge of attached shift plate 86. Consequently, vertical movement of pin 175 causes the wedge 122 and attached shift plate 186 to move vertically while still permitting horizontal displacement of these elements. Similarly, a pin 178 is mounted on the right end of the lower shift block 174 as viewed in FIG. 1 and is received in a slot 180 formed in the shift plate 88 and the associated attached wedge 124 connected thereto. Consequently, vertical movement of the second or lower threaded shift block 174 causes a resultant vertical movement of the wedge 122 and the attached shift plate 86 in an obvious manner. Since the movement of the two shift blocks 172 and 174 is always in opposite directions, it consequently follows that shift plates 86 and 88 are also always shifted in opposite directions. The employment of the wedge couples adjacent the top and the bottom of the shift plates 86 and 88 insures an absolute maintenance of parallel relationship between the shift plates at all times.

FIG. 1 illustrates an intermediate position of the wedge couples in which the individual wedge members are in alignment with each other and the discs 40 and 42 are in a median position between their maximum limits of movement on shaft 30. FIG. 4 illustrates a position in which the shift plates 86 and 88 have been moved to substantially their full limit of transverse movement to provide the maximum distance possible between the lapping discs 40 and 42. The distance between the discs 40 and 42 can be adjusted with extreme accuracy due to the small angle of inclination of the planes of sliding contact between the two wedge members forming each of the wedge couples.

In operation, air is initially supplied to the annular openings 58 and 62 and shaft 30 is rotated by the driving means (not shown). The lapping discs 40 and 42 are axially positioned with respect to each other by rotation of the adjustment knob 134. It should be noted that the rotation of shaft 30 is conveyed to each of the lapping discs by virtue of square portion 44 received in an axial mating opening in the lapping disc. However, the axial position of the disc along shaft 30 is easily adjusted as discussed previously.

FIG. 7 illustrates a second embodiment of the invention in which the lapping discs are rotated and oscillated about the axis of shaft 30. The oscillation is provided by virtue of the employment of a squared portion 44 that is eccentric with respect to the axis of shaft 30. Consequently, the lapping disc mounted on eccentric portion 44' is oscillated and rotated simultaneously. Otherwise, the embodiment illustrated in FIG. 7 is identical to the previously discussed first embodiment illustrated in FIGS. 1-6.

Both embodiments of this invention are normally employed with a conventional doctor plate construction surface on each lapping disc. The doctor plate construction is conventional and forms no part of this invention and is consequently not illustrated herein.

Similarly, since the lapping device forming the subject matter of this invention is capable of use with a wide variety of devices, no support means is illustrated for such devices. Devices such as micrometer anvils and some linear measuring gauges would have two surfaces respectively lapped at the same time by the two discs whereas other items being lapped would require the use of only one disc. It should be understood that any conventional support means can be employed for supporting the devices being lapped and it may be desirable in some instances to manually support such devices.

I claim:

1. A lapping machine comprising first and second lapping discs, means mounting said first and second lapping discs for rotation about a common axis of rotation, first and second biassing means each including an air cushion bearing means providing force for respectively biassing said first and second lapping discs outwardly away from each other along said axis of rotation and first and second counter-biassing means for urging said lapping discs inwardly against the biassing force exerted by said first and second biassing means for positioning said lapping discs in a position in which the axial forces exerted on said discs cancel each other.

2. The invention of claim 1 additionally including means for adjusting the axial distance between said air cushion means so as to consequently adjust the axial distance between said first and second lapping discs.

3. The invention of claim 2 wherein said means for adjusting the axial distance between said air cushion means include first and second shift plates each having one of said air cushion means fixedly attached thereto and a first wedge block couple extending between said shift plates for moving said shift plates along the axis of rotation upon movement of said plates in opposite directions normal to said axis of rotation.

4. The invention of claim 3 additionally including adjustment means for moving said first plate in a first direction while simultaneously moving said second plate in a second direction perpendicular to said axis to consequently adjust the axial distance between said lapping discs.

5. The invention of claim 4 wherein said first wedge block couple is adjacent a first end of said shift plates and additionally including a second wedge block couple extending between the other end of said shift plates for providing an absolute parallel relationship between said shift plates.

6. The invention of claim 5 wherein each of said wedge block couples includes first and second wedge members engageable with each other along plates of sliding contact with one of said wedge members including a male dovetail member received within a female dovetail slot of the other wedge member with said planes of sliding contacts being parallel with respect to each other.

7. The invention of claim 6 wherein said adjustment means for moving said first plate in a first direction while simultaneously moving said second plate in a second direction perpendicular to said axis includes a manual adjustment knob drivingly connected to an axially fixed rotatable rod having a first threaded portion with threads of one orientation and a second threaded portion with threads of opposite orientation to the threads on said first threaded portion with a first threaded shift block received on the first threaded portion and a second threaded shift block received on the second threaded portion and means connecting said first threaded shift block to said first shift plate and means connecting said second shift block to said second shift plate so that rotation of said rotatable rod causes said shift plates to move in opposite directions.

8. The invention of claim 7 wherein said means connecting said first shift block to said first shift plate and said second shift block to said second shift plate comprises pin means oriented perpendicular to the axis of rotation of said lapping discs and extending from said shift blocks and receivable within respective slots formed respectively in each of said shift plates.

9. The invention of claim 8 wherein each of said air cushion means includes an annular groove formed in a planar surface engaging one side of said lapping discs and connected to a passageway for receiving pressurized air at a sufficiently high pressure as to cause pressurized air from within said annular groove to escape radially between the surface of the bearing and the surface of the lapping disc to prevent metal-to-metal contact between the bearing surface and the surface of the lapping disc.

10. The invention of claim 2 wherein said means mounting said first and second lapping discs for rotation about a common axis of rotation comprises shaft means having an eccentric portion for supporting said lapping discs so that the axes of said lapping discs are eccentric with respect to the axis of said shaft means.

11. The invention of claim 10 wherein said means for adjusting the axial distance between said air cushion means includes first and second shift plates each having one of said air cushion means fixedly attached thereto and a first wedge block couple extending between said shift plates for moving said shift plates along the axis of rotation upon movement of said plates in opposite directions normal to said axis of rotation.

12. The invention of claim 11 additionally including adjustment means for moving said first plate in a first direction while simultaneously moving said second plate in a second direction perpendicular to said axis to consequently adjust the axial distance between said lapping discs.

13. The invention of claim 12 additionally including a second wedge block couple extending between the other end of said shift plates for providing an absolute parallel relationship between said shift plates.

14. The invention of claim 13 wherein each of said wedge block couples include first and second wedge members engageable with each other along planes of sliding contact with one of said wedge members including a male dovetail member received within a female dovetail slot of the other wedge member with said planes of sliding contact being parallel with respect to eachother.

15. The invention of claim 14 wherein said adjustment means for moving said first plate in a first direction while simultaneously moving said second plate in a second direction perpendicular to said axis includes a manual adjustment knob drivingly connected to an axially fixed rotatable rod having a first threaded portion with threads of one orientation and a second threaded portion with threads of opposite orientation to the threads on said first threaded portion with a first threaded shift block received on the first threaded portion and a second threaded shift block received on the second threaded portion and means connecting the first threaded shift block to said first shift plate and means connecting said second shift block to said second shift plate so that rotation of said rotatable rod causes said shift plates to move in opposite directions.

16. The invention of claim 15 wherein said means connecting said first shift block to said first shift plate and said second shift block to said second shift plate comprises pin means oriented perpendicular to the axis of rotation of said lapping discs and extending from said shift blocks and receivable within respective slots formed respectively in each of said shift plates,

17. A lapping machine having a lapping disc, means mounting said lapping disc for rotation about an axis of rotation, air cushion biassing means for biassing said disc along said axis of rotation, means for adjusting the position of said air cushion biassing means along said axis of rotation and counter-biassing means for urging said lapping disc inwardly against the biassing force exerted by said air cushion biassing means for positioning said lapping disc in a position at which the axial forces exerted on said disc cancel each other.

18. The invention of claim 17 wherein means for adjusting the position of said air cushion means includes a wedge couple formed of first and second wedge members movable transversely with respect to said axis of rotation for adjusting the position of said air cushion biassing means. 

1. A lapping machine comprising first and second lapping discs, means mounting said first and second lapping discs for rotation about a common axis of rotation, first and second biassing means each including an air cushion bearing means providing force for respectively biassing said first and second lapping discs outwardly away from each other along said axis of rotation and first and second counter-biassing means for urging said lapping discs inwardly against the biassing force exerted by said first and second biassing means for positioning said lapping discs in a position in which the axial forces exerted on said discs cancel each other.
 2. The invention of claim 1 additionally including means for adjusting the axial distance between said air cushion means so as to consequently adjust the axial distance between said first and second lapping discs.
 3. The invention of claim 2 wherein said means for adjusting the axial distance between said air cushion means include first and second shift plates each having one of said air cushion means fixedly attached thereto and a first wedge block couple extending between said shift plates for moving said shift plates along the axis of rotation upon movement of said plates in opposite directions normal to said axis of rotation.
 4. The invention of claim 3 additionally including adjustment means for moving said first plate in a first direction while simultaneously moving said second plate in a second direction perpendicular to said axis to consequently adjust the axial distance between said lapping discs.
 5. The invention of claim 4 wherein said first wedge block couple is adjacent a first end of said shift plates and additionally including a second wedge block couple extending between the other end of said shift plates for providing an absolute parallel relationship between said shift plates.
 6. The invention of claim 5 wherein each of said wedge block couples includes first and second wedge members engageable with each other along plates of sliding contact with one of said wedge members including a male dovetail member received within a female dovetail slot of the other wedge member with said planes of sliding contacts being parallel with respect to each other.
 7. The invention of claim 6 wherein said adjustment means for moving said first plate in a first direction while simultaneously moving said second plate in a second direction perpendicular to said axis includes a manual adjustment knob drivingly connected to an axially fixed rotatable rod having a first threaded portion with threads of one orientation and a second threaded portion with threads of opposite orientation to the threads on said first threaded portion with a first threaded shift block received on the first threaded portion and a second threaded shift block received on the second threaded portion and means connecting said first threaded shift block to said first shift plate and means connecting said second shift block to said second shift plate so that rotation of said rotatable rod causes said shift plates to move in opposite directions.
 8. The invention of claim 7 wherein said means connecting said first shift block to said first shift plate and said second shift block to said second shift plate comprises pin means oriented perpendicular to the axis of rotation of said lapping discs and extending from said shift blocks and receivable within respective slots formed respectively in each of said shift plates.
 9. The invention of claim 8 wherein each of said air cushion means includes an annular groove formed in a planar surface engaging one side of said lapping discs and connected to a passageway for receiving pressurized air at a sufficiently high pressure as to cause pressurized air from within said annular groove to escape radially between the surface of the bearing and the surface of the lapping disc to prevent metal-to-metal coNtact between the bearing surface and the surface of the lapping disc.
 10. The invention of claim 2 wherein said means mounting said first and second lapping discs for rotation about a common axis of rotation comprises shaft means having an eccentric portion for supporting said lapping discs so that the axes of said lapping discs are eccentric with respect to the axis of said shaft means.
 11. The invention of claim 10 wherein said means for adjusting the axial distance between said air cushion means includes first and second shift plates each having one of said air cushion means fixedly attached thereto and a first wedge block couple extending between said shift plates for moving said shift plates along the axis of rotation upon movement of said plates in opposite directions normal to said axis of rotation.
 12. The invention of claim 11 additionally including adjustment means for moving said first plate in a first direction while simultaneously moving said second plate in a second direction perpendicular to said axis to consequently adjust the axial distance between said lapping discs.
 13. The invention of claim 12 additionally including a second wedge block couple extending between the other end of said shift plates for providing an absolute parallel relationship between said shift plates.
 14. The invention of claim 13 wherein each of said wedge block couples include first and second wedge members engageable with each other along planes of sliding contact with one of said wedge members including a male dovetail member received within a female dovetail slot of the other wedge member with said planes of sliding contact being parallel with respect to each other.
 15. The invention of claim 14 wherein said adjustment means for moving said first plate in a first direction while simultaneously moving said second plate in a second direction perpendicular to said axis includes a manual adjustment knob drivingly connected to an axially fixed rotatable rod having a first threaded portion with threads of one orientation and a second threaded portion with threads of opposite orientation to the threads on said first threaded portion with a first threaded shift block received on the first threaded portion and a second threaded shift block received on the second threaded portion and means connecting the first threaded shift block to said first shift plate and means connecting said second shift block to said second shift plate so that rotation of said rotatable rod causes said shift plates to move in opposite directions.
 16. The invention of claim 15 wherein said means connecting said first shift block to said first shift plate and said second shift block to said second shift plate comprises pin means oriented perpendicular to the axis of rotation of said lapping discs and extending from said shift blocks and receivable within respective slots formed respectively in each of said shift plates.
 17. A lapping machine having a lapping disc, means mounting said lapping disc for rotation about an axis of rotation, air cushion biassing means for biassing said disc along said axis of rotation, means for adjusting the position of said air cushion biassing means along said axis of rotation and counter-biassing means for urging said lapping disc inwardly against the biassing force exerted by said air cushion biassing means for positioning said lapping disc in a position at which the axial forces exerted on said disc cancel each other.
 18. The invention of claim 17 wherein means for adjusting the position of said air cushion means includes a wedge couple formed of first and second wedge members movable transversely with respect to said axis of rotation for adjusting the position of said air cushion biassing means. 